Currently, as leading cause of mortality in western countries cardiovascular diseases (CVD) are largely responsible for the ever increasing costs of healthcare systems.
Research studies on hypertension have, so far, generally focused on vascular resistance and small arteries. The high prevalence of systolic hypertension in patients older than 50 years and the development of noninvasive Doppler and echo tracking techniques have made it possible to determine large-artery stiffness with a high degree of reproducibility. Increased arterial stiffness and disturbed wave reflections are the basis for understanding reduced aortic elasticity and systolic hypertension, particularly in older people. This hemodynamic pattern results from mechanical factors and other pressure-independent risk factors, such as diabetes mellitus, renal failure, obesity and severe atherosclerosis.
The roles of arterial stiffness and wave reflections in hypertension have been elucidated by modern interpretations of the blood-pressure curve in relation to its propagation, mechanisms of systolic-blood-pressure amplification, and the pulse-pressure amplitude. New predictors of cardiovascular risk have been identified, such as increased pulse pressure and pulse-wave velocity as well as disturbed wave reflections, all of which are independent predictors of cardiovascular risk that are more powerful than either systolic or diastolic blood pressure alone. Therapeutic trials are investigating ways to reduce stiffness, and thereby allow the selective reduction of systolic and pulse pressure in hypertensive patients with or without advanced renal failure.
Because several studies have recently highlighted the important role that arterial stiffness plays in the development of CVD, and since central stiffness has been shown to be the best independent predictor of both cardiovascular and all-cause mortality, stiffness might be considered to be the missing vascular-related parameter in ambulatory cardiovascular monitoring. However, the only available technique for measuring arterial stiffness non-invasively so far is the so-called pulse wave velocity (PWV).
EP 2 000 084 A1 discloses an apparatus for obtaining pulse wave velocity information including a light-emitting unit, an image sensor configured to capture images, in time sequence, relating to a living body, a lens, an extreme-occurrence-time obtaining unit configured to obtain times T1 and T2 at which extremes occur in time sequence with respect to brightness values of a first region and a second region of each of the captured images, the time T1 being obtained for one of the first regions and the time T2 being obtained for one of the second regions, and a PWV calculation unit configured to calculate a pulse wave velocity according to expression P=(Y L/f)/(T2−T1), where Y represents a distance on the image sensor, the distance corresponding to a distance between the first region and the second region, f represents the focal length of the lens, and L represents a distance between the lens and the living body.
EP 2 631 874 A1 discloses a system and method for determining an arterial pulse transit time of a subject of interest in a remote sensing environment. A video imaging system is used to capture a time varying source images of a proximal and distal region of a subject intended to be analyzed for arterial pulse transit time. A time series signal for each of the proximal and distal regions is extracted from the source images and a phase of each of the extracted time series signals is computed. A difference is then computed between these phases. This phase difference is a monotonic function of frequencies in the signals. From the monotonic function, an arterial pulse transit time of the subject is extracted. The subject's arterial pulse transit time is then communicated to a computer system. The computer system determines blood pressure, blood vessel blockage, blood flow velocity, or a peripheral neuropathy.
US 2010/0195473, WO 2012/093320 A2 and the article of W. Verkruijsse et al.: “A novel biometric signature: multi-site, remote (>100 m) photo-plethysmography using ambient light”, Technical Note PR-TN 2010/00097, March 2010, disclose further developments of the applicant regarding a device and method for remote photo-plethysmography.
WO 2013/1663341 A1 discloses physiological characteristic detection based on reflected components of light.
DE 197 41 982 discloses a system for local non-invasive functional indicating of dermal blood perfusion.
US 2013/0046192 A1 discloses an image-based PWV measurement device and method.